Lecture Outline - Sulfuric Acid - History of Manufacture Development - Manufacture - Oleum Production - Heat Integration Issues / By-products - Markets - Usage in Caprolactam Manufacture

History of Manufacture of Sulfuric Acid One of the oldest industrially applied processes. Discovered by a Persian alchemist in the tenth century. Saltpeter and sulfur were mixed in a glass container and burned in a moist atmosphere. Acid was collected from the condensed vapors. In England, 1746, the lead chamber reactor was invented. This invention allowed for higher production rates (<78%). In England, 1831, a patent was filed that described the oxidation of sulfur dioxide over a platinum catalyst, the Contact Process. This new process increased yields of reaction from 70 to above 95%. In 1913 BASF was granted a patent for the use of vanadium pentoxide as a catalyst for the Contact Process By the 1930’s vanadium pentoxide was becoming the dominate catalyst used because of insensitivities to poisons and lower cost. In 1960 a patent application was filed by Bayer using the so called double-catalyst process (double absorption).

World Supply / Demand for Sulfuric Acid (thousands of metric tons, 100% H 2 SO 4 )

World Production of Sulfuric Acid

Manufacture

Oxidation of Sulfur Air 93% H 2 SO 4 Sulfur 10-12% SO 2 Steam Water Primary Generation of SO 2 -79% Combustion of Sulfur -9% Recovery from Metallurgic Processes - 5% Regeneration of Spent Acids Process: - Air drying tower with acid - Sulfur is injected into burner - Reaction Temperature 2000°F - Exothermic reaction must be cooled - Steam recovered

Oxidation of Sulfur Dioxide Contact Process: -Vanadium pentoxide catalyst - Exothermic Rxn - Multiple Steps with cooling in between - Double absorption - Heat integration Gas Cooling SO 3 Gas SO 2 Gas

Oxidation of Sulfur Dioxide  Because of the large effect temperature plays on the reaction, multiple catalyst layers had to be used with cooling between each step.  Additionally, as the partial pressure of SO 3 increases further reaction is limited.  This was overcome by removing the SO 3 after the third stage to drive the reaction to completion. Gas Cooling SO 3 Gas SO 2 Gas 93% H 2 SO 4 SO 2 Gas

Oxidation of Sulfur Dioxide Kinetic Effects - Oxidation of sulfur dioxide is slow and reversible - The reaction requires a catalyst and 426.7°C temperatures -The reaction is exothermic and sensitive to excessive heat Equilibrium Constant (The degree at which the reaction proceeds is temp. dependent) log Kp = T T = absolute temp. in kelvin Kp = equilibrium constant as a function of partial pressure of gases Kp = ( P SO 3 ) P SO 2 P O 2 0.5

Oxidation of Sulfur Dioxide Temperature Profile Gas Cooling SO 3 Gas SO 2 Gas 93% H 2 SO 4 SO 2 Gas 75 C 200 C 430 C 510 C 125 C

Oxidation of Sulfur Dioxide Temperature Profile

Oxidation of Sulfur Dioxide Typical Catalyst Distribution

Overall Production Scheme

Oleum Production  Sulfuric acid with additional SO 3 absorbed  20% Oleum contains 20% SO 3 by weight in the oleum  Common strengths of oleum are 20, 30, 40, 65 percent.  To produce 20 and 30 percent oleum, only requires an additional absorption tower.  Oleum is used in reactions where water is excluded SO 3 + H 2 SO 4 H 2 S 2 O 7 (disulfuric acid)

Reaction By-products / Heat Integration By-products  57 to 64% of the energy input generates steam  Steam energy is used to drive the turbine that supplies power to the main air blower  Additional steam remaining is tolled internally for other plant operations  SO 2 /SO 3 is vented in small amounts and is federally regulated. Heat Integration  Steam is used to pre-heat and vapor from the absorption towers used to cool  Minimizes the cost of manufacturing to maximize the profit.

Production Considerations  Metal corrosion is a big issue in the manufacture of sulfuric acid.  Special alloy metals must be used to guard against excessive corrosion.  Nickel, chromium, molybdenum, copper, an silicon are the most important elements that enhance corrosion resistance of alloys.  Important variables for corrosion  Concentration of the acid  Temperature of service  Speed of flow in pipes and equipment  Alloy element make-up

Markets for Sulfuric Acid  The fertilizer market is the largest U.S. single use for sulfuric acid and consumes percent of all produced.  Second is the organic chemical industry. Production of plastics and synthetic fibers are examples.  Production of TiO 2 consumes large quantities of sulfuric acid. TiO 2 is a white pigment used in paints and plastics.  In the metal industry sulfuric acid is used for pickling ferrous and non- ferrous materials and in the recovery of copper, nickel, and zinc from low-grade ores.  Finally, the petroleum industry uses acid as a catalyst for various reactions.

Acid Strengths Associated End Uses

Usage in Caprolactam Manufacture Production and consumption figures for caprolactam manufacture